1. Field of the Invention
The present invention relates in general to an active matrix substrate for a liquid crystal display (LCD) and method of forming the same. In particular, the present invention relates to a liquid crystal display having a high pixel aperture ratio (pixel opening size) and method of forming the same.
2. Description of the Related Art
Generally, LCDs have an upper and a lower substrate with electrodes thereon. These substrates are sealed with adhesive materials, and a liquid crystal material is sealed between these two substrates. Before the liquid crystal is injected between the two substrates, spacers are sprayed between the substrates in order to hold a constant distance therebetween. Conventionally, many TFTs are formed above the lower substrate as switching devices. Each TFT has a gate electrode connected to a scanning line, a drain electrode connected with a signal line, and a source electrode connected to a pixel electrode. The lower substrate is also called an active matrix substrate. The upper substrate includes a color filter and a common electrode.
The higher the pixel aperture ratio of a LCD, the higher the display transmission. Thus, by increasing the pixel aperture ratio of a LCD, transmission may be increased using the same backlight power, or alternatively, the backlight power consumption may be reduced while maintaining the same display transmission.
In order to enhance the pixel aperture ratio, a thicker insulating layer is formed over source and drain electrodes before forming pixel electrodes, thus, the pixel electrodes are formed over the insulating layer so as to overlap portions of the address lines, as disclosed in U.S. Pat. Nos. 5,955,744, 5,780,871, 5,641,974. Thus, the capacitance between pixel electrodes and underlying conducting material can be reduced, and an effective display area, i.e. the area of the pixel electrode, can be enlarged.